Heretofore, as a photosensitive material for an electrophotographic photoreceptor, inorganic photoconductive material such as selenium, selenium alloys, zinc oxide and sulfurized cadmium have mainly been employed.
Recently, organic photosensitive materials which can be selected those suitable for its purpose such as high productivity, non-polluting and inexpensive cost and targeted performances have come to be used. Among them, a function-separation type photoreceotr which is a combination of a charge generating material and a charge transparting material can noticeably improve sensitivity which had been a shortcoming of photoreceptors using organic photoconductive materials. Therefore, it is specifically noted.
However, if the above-mentioned function-separation type high sensitivity photoreceptor is applied to a so-called Carlson process, the surface charge is reduced due to charge injecting from the conductive layer. Namely, together with reduction of charge property, charge maintaining property deteriorates. In addition, after repeated use, the above-mentioned properties tend to be further deteriorated. Accordingly, uneven density and fogging occur on the image. In the case of reversal development, background contamination occurs. Due to repeated using and using for a long time, the problems commonly becomes worse.
Therefore, in order to overcome the above-mentioned problems, various studies to provide a means wherein an intermediate layer is provided between a conductive layer and a photosensitive layer have heretofore been proposed. For example, an intermediate layer employing a nylon resin, a vinylacetic acid resin, a polyvinyl alcohol resin, a resin wherein aluminum oxide was dispersed and a resin wherein tin Oxide have been studied. In addition, recently, ceramic-containing intermediate layers using an organic metal compound and a silane coupling agent have also been developed.
However, even if the above-mentioned intermediate layer was adopted, when a combination with the conductive layer is not appropriate, due to initial and repeated use, reduction of conductivity, increase of dark decay rate and the occurrence of fogging after using for a long period were observed so that it was shown that solution of the problems is not sufficient.
In an electrophotographic image forming apparatus, a electrostatic image forming material which plays an important role in producing an electrostatic latent image and in a developing process (typically, an electrophotographic photoreceptor. Hereinafter, it may be referred to as a photoreceptor) is necessary. In a transferring process which transfers the prepared toner image onto plain paper, a transferring material or an intermediate transferring material is necessary.
In order to execute their function, the electrostatic image forming material, the transferring material or the intermediate transferring material must move in prescribed timing and at a prescribed speed while not changing the interval and pressure condition with chargers, exposure devices, developing devices, charge-eliminating device or the cleaning devices, which are located around them. For repeated use, when one cycle of an image forming process is completed, they must return to the initial position for the next image forming cycle. In order to carry out the series of movements smoothly, and in order to use expensive member such as the photoreceptor more effectively, in apparatus for a practical use, the photoreceptor (electrostatic latent image forming material), the transferring material and the intermediate transferring material are almost cylindrical (drum-shaped). As a substance used therefor, metal material such as aluminum is generally used.
On the other hand, plastic is considered to be a preferable material since it is light and its cost is inexpensive. However, it is not easy to manufacture electrostatic latent image forming cylinder with high accuracy and with high effectiveness in terms of industrial setting. The major factor was that a method to manufacture a 30-200 mm diameter cylindrical subtrate simply at high accuracy could not be discovered. Therefore, accuracy had to be maintained by cutting and abrading the surface thereof after manufacturing the cylindrical subtrate, resulting in reduction of producibility and at an increase of cost. In addition, there was another shortcoming in that it is weak to heat and most solvent. In addition to accuracy on the surface of the subtrate, deformation due to stress and aging has also become a problem.
However, in the case of the image forming apparatus constituted of image exposing from inside of the photoreceptor as detailed later, the cylindrical subtrate of electrostatic latent image forming material must be transparent against light for exposure. Therefore, metals cannot be used as a material for a subtrate.
In addition, it is necessary to provide a transparent layer having conductivity on a cylindrical substrate which is also an insulating material. As a typical technology to provide conductivity, a method to deposit or spatter metal such as aluminum or ITO (Indium tin oxide) or other metal oxides and a method to disperse powdered metal and metal oxide fine particles in a resin and cause it in an ink state for coating are employed. However, the former method results in deformation wherein dimensional accuracy of the cylindrical subtrate due to heat is lost and increase in cost, and the latter method results in an increase of the number of processes and modification of the production facility.
Accordingly, though an image forming method wherein an image is exposed to light from inside is excellent as an apparatus, it was actually difficult to be come into practice.
A first object of the present invention is to provide an excellent electrophotographic photoreceptor having no reduction of electrification property between the initial cycle and after repeated use, no reduction of charge maintaining property, no occurrence of fogging, and an image forming method and an apparatus using the same.
A second object is to provide a cylindrical subtrate for an image forming apparatus, having a conductive layer on its surface, which can be manufactured effectively in an industrial setting, which has high surface accuracy, overall strength and which has sufficiently high transparency as necessary and a method for manufacturing therefor and an electrophotographic photoreceptor and an image forming apparatus using the same.